High-Entropy Alloys Explained

TECHNOLOGY EXPLAINER

High-Entropy Alloys
— how far “stabilised by entropy” can be said, and reading values with composition, processing and test temperature

High-entropy alloys (HEAs) have been defined as alloys that mix five or more elements, each at 5–35 at.%. The explanation that “the more elements, the larger the configurational entropy, and the more a simple solid solution is stabilised” is widely known, but a later review concludes that this “effect” is not supported by present data. Even so, experiments with changed compositions have confirmed that Cr-Mn-Fe-Co-Ni and Cr-Co-Ni alloys gain strength, ductility and fracture toughness together at the temperature of liquid nitrogen (77 K). This article sets out the definition and configurational entropy, the assessment of the “core effects”, where solid solutions part from intermetallics, and examples in cryogenic, high-temperature, lightweight, additive-manufactured, corrosion, hydrogen and radiation settings, within what primary sources say, always with composition (at.%), processing state and test temperature.

Built from peer-reviewed papers (Science, Nature, Nature Communications, Acta Materialia, Entropy and others) and official pages of standards bodies (ISO and JISC) / Checked 10 October 2026

Fig. 1 Conceptual image generated with ImageGen. A furnace illustrates alloy specimen preparation from multiple elements. External specimens are cooled; mixing alone does not establish a single phase or high performance. Not actual facilities, products or measured results.

What this article covers

The short version
Definition and configurational entropy (our calculation: ΔSconf and the size of the entropy term)
The “four core effects”, and where the assessment stands
Solid solution or intermetallic (our calculation: VEC and rule-of-mixtures density)
Alloys that get stronger at cryogenic temperature — CrMnFeCoNi and CrCoNi
High temperature, light weight, strength and ductility together — refractory HEAs, lightweight HEAs, TRIP type
Additive manufacturing (laser powder bed fusion)
Corrosion, hydrogen and radiation
Limits, and what could not be confirmed
How to read the evaluation standards
Glossary / References / Claim-to-source audit

How claims are labelled in this article

Sourced = stated in published material (link given)
Our calculation = a figure this article derived, with the assumptions spelled out
Not yet confirmed = a plan or schedule whose record has not been confirmed
Materials-design interpretations are marked separately as Commentary. Inference is shown in bold. Compositions are written in atomic fraction (at.%); an equiatomic alloy is written as “20 at.% each”.

How to read the numbers in this article

HEA figures are laboratory results fixed by composition, route (melting, mechanical alloying, additive manufacturing), heat treatment, grain size, test temperature and strain rate, and specimen shape. Please do not read the value for one alloy as a property of the whole class called “HEA”. Words such as “excellent” or “universal” mean something only when the conditions are stated and the comparison is with another alloy under the same test. This article does not rank particular alloys, products or companies, and gives no medical, safety or investment advice. The checking date is 10 October 2026.

1. The short version

An HEA is defined as “five or more elements, 5–35 at.% each”, and for an equiatomic alloy the configurational entropy is R ln N. It is 1.61R for N = 5 and 2.57R for N = 13. Conventional alloys range from about 0.22R for low-alloy steels, to about 1.15R for stainless steels, to at most about 1.37R for superalloysSourced [Source 4]
A review judges that “entropy stabilises the solid solution” is not supported as an “effect” by present data. A 20-element equiatomic alloy was a brittle multiphase materialSourced [Sources 3, 6]. Examples are reported in which replacing a single element in a five-element alloy produces an intermetallic [Source 4]
Even so, CrMnFeCoNi and CrCoNi gained strength, ductility and fracture toughness from room temperature to 77 K (tensile strength of CrMnFeCoNi 763 to 1,280 MPa; KJIc of CrCoNi above 200 MPa√m at room temperature and 275 MPa√m at 77 K)Sourced [Sources 5, 6]. But the comparison is not between specimens of matched processing and grain size. Read the values as the result for that composition and state, not for a class of alloys

The single most important line

Read it not as “high entropy, therefore excellent”, but as “the composition space widened, and some compositions gave good values under particular cryogenic or high-temperature conditions”. An alloy’s value means something only with composition (at.%), route, heat treatment, grain size and test temperature together. The word “HEA” guarantees none of them (Commentary).

2. Definition and configurational entropy

In setting out a strategy to design and evaluate HEAs for structural use, Miracle et al. (Entropy, 2014) take as the standard definition of an HEA an alloy with five or more elements, each at 5–35 at.%, and write the configurational entropy of an equiatomic alloy as ΔS_conf = R ln N (R the gas constant, N the number of elements)Sourced [Source 4]. By the same paper, N = 5 gives 1.61R and N = 13 gives 2.57R, and conventional alloys have about 0.22R for low-alloy steels, about 1.15R for stainless steels and up to about 1.37R for superalloys. The paper also records a practical guide of ΔS_conf of 1.5R or more [Source 4].

Yeh et al. (2004) used the name “high-entropy alloys” and showed preliminary results in which multi-principal-element alloys made by established processing had simple crystal structures, nanostructures and promising mechanical properties [Source 1]. In the same year Cantor et al. reported microstructural development in equiatomic multicomponent alloys, and a later paper by Gludovatz et al. cites that an alloy of 20 elements in equal ratios gave a very brittle multiphase microstructure [Sources 2, 6].

Our calculation 1: configurational entropy and the size of the entropy term

For an equiatomic alloy of N elements, ΔS_conf = R ln N with R = 8.314 J/(mol·K)Our calculation.

ΔS_conf/R: 0.69 for N = 2, 1.10 for 3, 1.39 for 4, 1.61 for 5, 1.79 for 6, 2.08 for 8, 2.30 for 10, 2.57 for 13, 3.00 for 20
A non-equiatomic example: for Al₂₀Li₂₀Mg₁₀Sc₂₀Ti₃₀ (at.%), ΔS_conf/R = −Σ x ln x = about 1.56 (less than 1.61 for five equal elements, but above 1.5)
The entropy term −TΔS_conf (kJ/mol): at 1,000 K, 5.76 for N = 2, 13.38 for N = 5 and 21.32 for N = 13. At 1,500 K, 8.64 for N = 2, 20.07 for N = 5 and 31.99 for N = 13. At 300 K, even N = 5 gives only 4.01
What it competes with: Miracle et al. put the mean free energy of formation ΔG of more than 1,000 binary compounds at about −41 kJ/mol (median −36 kJ/mol) [Source 4]. The entropy term of an equiatomic N = 5 alloy at 1,000 K is about 13 kJ/mol, about one third of that mean

Assumptions and limits: this calculates only the configurational entropy, as the upper limit for ideal mixing. It does not include the mixing enthalpy, the strain energy from atomic-size differences, or phase changes with temperature. A large entropy term does not mean the solid solution is stable (Sections 3 and 4).

Fig. 2 Drawing including our calculation (vector graphic). A bar chart of the configurational entropy ΔS_conf/R of equiatomic alloys for N = 2 to 13 elements. The guides for conventional alloys (low-alloy steels, stainless steels, superalloys) are as stated in the paper by Miracle et al. [Source 4]. These are not measured values of real alloys, and they do not show the conditions under which a solid solution is stable.

Fig. 3 Drawing including our calculation (vector graphic). Lines of the entropy term −TΔS_conf for equiatomic alloys with N = 2, 5 and 13 from 300 to 1,500 K, and the mean ΔG of binary compounds [Source 4]. It does not include the mixing enthalpy and does not show phase stability itself.

Materials engineer’s view 1: read the entropy term next to its rival, the enthalpy

The configurational-entropy term grows in proportion to temperature (Fig. 3) and favours the solid solution at high temperature. Against it, forming an intermetallic brings an enthalpy gain, and Miracle et al. estimate the mean ΔG of binary compounds at about −41 kJ/mol [Source 4]. The same paper shows that the share of binary intermetallics that lose stability rises with temperature (about 10–15% at 300 K, about 20–32% at 600 K, about 40–60% at 1,500 K), and that the share of HEAs that become single-phase is about one third at 600 K and about two thirds at 1,500 K [Source 4] (the population and method of that analysis were not checked in detail here).

From a materials viewpoint this reads as “the higher the temperature, the more likely a solid solution, but even at 1,500 K about one third do not become single-phase“. Whether a product is single-phase at its service temperature also depends on the casting and heat-treatment temperatures and the cooling rate (Commentary).

3. The “four core effects”, and where the assessment stands

Introductions to HEAs often explain their character through four ideas: the “high-entropy effect”, the “lattice-distortion effect”, “sluggish diffusion” and the “cocktail effect” (this article’s own arrangement; the source of the name “four” was not confirmed here). What could be confirmed in primary sources is as follows.

Fig. 4 Conceptual diagram (vector graphic). The four ideas commonly voiced in HEA introductions (our arrangement), set beside the assessment found in the cited sources [Sources 3, 4, 6, 7, 10]. It is not the full conclusion on each effect; every source was checked only at the level of its abstract or part of its body.

High-entropy effect (configurational entropy stabilises the solid solution): Gludovatz et al. open their 2014 paper by presenting, as a rationale, that the configurational-entropy contribution in alloys with five or more major elements may stabilise the solid solution relative to multiphase microstructures [Source 5]. By contrast, the review by Miracle and Senkov (Acta Materialia, 2017) says in its abstract that the entropy effect is not supported by the data, and that sluggish diffusion is not supported eitherSourced [Source 3]. The 2016 paper by Gludovatz et al. likewise says, from the 20-element alloy being a brittle multiphase material, that high configurational entropy by itself cannot suppress the formation of intermetallic phases made of the constituent elements [Source 6]
Sluggish diffusion: Tsai et al. published a paper on diffusion in Co-Cr-Fe-Mn-Ni alloys (only the title was checked; the body was not) [Source 7]. The review states that “sluggish diffusion” is not supported by the data either [Source 3]
Lattice-distortion effect and cocktail effect: no statement that tests these was found in the body of the primary sources this article could check. Because they could not be confirmed, no assessment is written. In the data compilation on refractory HEAs by Couzinié et al., density and Young’s modulus are computed by the rule of mixtures [Source 10] (whether the rule holds for other properties was not checked here)

Where the review stands

The review by Miracle and Senkov (2017) states in its abstract that it assessed microstructure using experimental data from 408 alloys and two computational datasets from the CALPHAD method. Its conclusions include that classical thermodynamic concepts are unchanged but trends in multi-principal-element alloys can differ from simpler alloys, that research once strongly focused on 3d transition-metal alloys now spans seven distinct families of complex concentrated alloys (CCAs), and that designing alloy families by choosing elements for a specific purpose has begun to emergeSourced [Source 3]. It also says that austenitic stainless steels and nickel alloys with three or more principal elements fall within “multi-principal-element alloys (MPEAs)” [Source 3] (this article cites only within the scope of these abstracts).

4. Solid solution or intermetallic — mixing enthalpy and valence electron concentration

On what decides a single-phase solid solution, Guo et al. studied the relation between the physicochemical and thermodynamic properties of the alloying components and phase stability, and report that the mixing enthalpy is the key factor controlling whether solid solutions or compounds form and that the stability of fcc and bcc solid solutions is well delineated by the valence electron concentration (VEC)Sourced [Source 8] (the boundary values were not checked in the body here). Miracle et al. give an example in which CoCrFeMnNi forms a single-phase solid solution whereas TiCrFeMnNi, which replaces Co with Ti in the same five-element set, forms intermetallics [Source 4].

Our calculation 2: VEC and a rule-of-mixtures density estimate

VEC is the mean of the valence electron counts of the elements (Co 9, Cr 6, Fe 8, Mn 7, Ni 10, Nb 5, Mo 6, Ta 5, W 6, V 5, Al 3, Li 1, Mg 2, Sc 3, Ti 4), weighted by atomic fractionOur calculation. The rule-of-mixtures (ROM) density was found from ρ = Σ(x_iM_i) / Σ(x_iM_i/ρ_i) (x: atomic fraction, M: atomic mass, ρ_i: density of the element). The elemental densities used were Co 8.90, Cr 7.19, Fe 7.87, Mn 7.43, Ni 8.91, Nb 8.57, Mo 10.28, Ta 16.65, W 19.25, V 6.11, Al 2.70, Li 0.534, Mg 1.74, Sc 2.99 and Ti 4.51 g/cm³ (standard values used in this article).

Alloy (at.%)	VEC (our calculation)	Rule-of-mixtures density (g/cm³, our calculation)	Reported structure and route	Source
CoCrFeMnNi (20 each)	8.0	about 8.0	Single-phase fcc solid solution; single-phase after casting and homogenisation and after recrystallisation [6]	[5, 6]
NbMoTaW (25 each)	5.5	about 13.6	Refractory HEA; mechanical properties reported (the structure was not confirmed here)	[9, 10]
VNbMoTaW (20 each)	5.4	about 12.4	Refractory HEA; mechanical properties reported (the structure was not confirmed here)	[9, 10]
Al₂₀Li₂₀Mg₁₀Sc₂₀Ti₃₀	2.8	about 2.67	Made by mechanical alloying; single-phase fcc during ball milling, transforming to single-phase hcp on annealing	[11]

The VEC and density columns are Our calculation; the structure and route column is Sourced (Gludovatz et al. [6], Youssef et al. [11]). The rule-of-mixtures density is not a measured density. VEC was reported by [8] as a guide to fcc/bcc stability; whether it predicts other structures (hcp) or intermetallics was not checked here.

Materials engineer’s view 2: “single-phase” needs a check of the state, not only the composition

That CoCrFeMnNi is single-phase is stated by Gludovatz et al. by citing work that confirmed it by X-ray diffraction and backscattered-electron images after casting and homogenisation, by transmission electron microscopy after recrystallisation, and by three-dimensional atom probe tomography (in the cast and homogenised state and after severe plastic deformation) [Source 6]. From a materials viewpoint, when you receive a value labelled “single-phase”, check (a) how the composition was analysed and the measured values (at.%), (b) whether the state is as-cast, homogenised, or worked and recrystallised, (c) how the phases were identified (X-ray diffraction, electron backscatter diffraction, transmission electron microscopy), and (d) the grain size (Commentary). Comparisons between specimens of unmatched grain size are not direct comparisons (the CrCoNi example in Section 5).

5. Alloys that get stronger at cryogenic temperature — CrMnFeCoNi and CrCoNi

The most closely studied HEA examples are CrMnFeCoNi (20 at.% each, often called the “Cantor alloy”) and CrCoNi (three elements at 33.3 at.% each), which removes Mn and Fe from it. The 2014 paper by Gludovatz et al. (Science) reports that CrMnFeCoNi is a single-phase fcc solid solution with tensile strength above 1 GPa and fracture toughness above 200 MPa√m, that its properties actually improve at cryogenic temperatures, and explains this by a shift from planar-slip dislocation activity at room temperature to deformation by mechanical nanotwinning as the temperature falls, giving continuous steady strain hardeningSourced [Source 5].

The 2016 paper by Gludovatz et al. (Nature Communications) reports that three-element CrCoNi is a single-phase fcc solid solution with a tensile strength of almost 1 GPa, a failure strain of about 70% and KJIc above 200 MPa√m at room temperature (293 K), and above 1.3 GPa, up to 90% and 275 MPa√m at 77 K [Source 6]. In the body of the paper, KJIc is 208 MPa√m (JIc = 212 kJ/m²) at 293 K and 273 MPa√m (JIc = 363 kJ/m²) at 77 KSourced [Source 6]. The same paper also says that from room temperature to 77 K CrMnFeCoNi rose in tensile strength from 763 to 1,280 MPa and in ductility from 0.5 to 0.7 (no unit given in the text), while KJIc stayed well above 200 MPa√m [Source 6]. The relation of “tensile strength above 1 GPa” in the 2014 abstract to 763 MPa at room temperature (perhaps a difference in conditions) was not checked in the body here.

Condition (CrCoNi in [6])	What is reported
Composition	Equiatomic CrCoNi (1/3 each of Cr, Co, Ni)
Route and processing	Arc melting, homogenisation at 1,200 °C for 24 hours, about 60% reduction, annealing at 800 °C for 1 hour
Grain size	A non-uniform grain size of 5–50 μm. The authors think the yield strength at 77 K being slightly below that of CrMnFeCoNi is due to this non-uniform grain size
Test temperature	293 K (room temperature), 198 K (dry ice and ethanol), 77 K (liquid nitrogen)
Specimens and mention of a standard	Tensile and C(T) specimens cut by electrical discharge machining. The C(T) specimens were fatigue pre-cracked and side-grooved and tested “in general accordance with ASTM E1820” (this article did not consult ASTM and cites it as a statement in the paper)
Fracture-toughness evaluation	The J-integral was measured as a function of crack growth at 293, 198 and 77 K (displacement control, 2 mm/min). KJIc at crack initiation is stated to have met the validity conditions of ASTM E1820

All Sourced (the body of Gludovatz et al. [Source 6]; the ASTM standard itself was not checked).

Our calculation 3: the change from 293 K to 77 K

Ratios of reported valuesOur calculation.

Tensile strength of CrMnFeCoNi: 1,280 / 763 = about 1.68 (about 68% higher)
KJIc of CrCoNi (body values): 273 / 208 = about 1.31 (about 31% higher)
Failure strain of CrCoNi: about 70% to up to 90%, a 20-point rise (a ratio of about 1.29). Tensile strength goes from about 1 GPa to above 1.3 GPa, a rise of more than 30%

Assumptions and limits: these are ratios of values from different papers and different specimens (different grain size and processing), not ratios within one test. For KJIc at 77 K both 273 and 275 are written; the body value 273 is used here.

Fig. 5 Conceptual image generated with ImageGen. Tensile testing at controlled temperature is combined with separate microstructural examination. Room-temperature and cryogenic properties need not coincide. Not actual facilities, products or measured results.

Fig. 6 Drawing (vector graphic). Reported tensile strength, failure strain and fracture toughness KJIc of CrMnFeCoNi and CrCoNi at 293 K and 77 K [Sources 5, 6]. The KJIc bars are drawn at the lower bound of the “above 200” statement. It places side by side values for specimens of different grain size and processing, and is not a direct comparison of the two alloys.

Materials engineer’s view 3: read cryogenic values by “deformation mechanism, grain size and test conditions”, not by “the alloy’s name”

Both papers explain the gain in strength and toughness at cryogenic temperature by continuous strain hardening from dislocation motion and deformation-induced nanotwins [Sources 5, 6]. What matters is therefore not the number “five elements” but a deformation mechanism that is probably linked to a low stacking-fault energy (the latter is Commentary and an inference beyond the papers’ statements). Miracle et al.’s review says that austenitic stainless steels and nickel alloys also belong to “multi-principal-element alloys” with three or more principal elements [Source 3]. When considering an HEA as a material, it therefore has to be compared with existing materials such as austenitic stainless steels at the same temperature, under the same test standard and at the same grain size. This article does not cite values for such comparison materials (an item that could not be confirmed). Cryogenic tension and fracture toughness also move with specimen size, how the pre-crack is made, side grooves, strain rate and coolant (liquid nitrogen, dry ice with ethanol), so check the scope of standards such as ISO 6892-1, ISO 12135 and JIS Z 2284 (the standard for elastic-plastic fracture toughness in liquid helium) against the test report (Section 10).

6. High temperature, light weight, strength and ductility together — refractory HEAs, lightweight HEAs, TRIP type

Refractory HEAs (NbMoTaW, VNbMoTaW and others)

The data article by Couzinié et al. (Data in Brief, 2018) organises the mechanical properties of 122 refractory HEAs (RHEAs) and refractory complex concentrated alloys (RCCAs) reported from 2010 to January 2018 by composition, type of microstructure, metallurgical state, computed density, type of loading and yield stress at each test temperature. It distinguishes RHEAs (five or more elements, 5–35 at.% each) from RCCAs (three or more principal elements, with concentrations extended beyond 35%)Sourced [Source 10]. Density and Young’s modulus are computed by the rule of mixtures [Source 10]. Senkov et al. reported the mechanical properties of Nb₂₅Mo₂₅Ta₂₅W₂₅ and V₂₀Nb₂₀Mo₂₀Ta₂₀W₂₀ (only the title was checked; the values were not) [Source 9]. The review by Miracle and Senkov says in its abstract that some alloys based on refractory elements may extend the range in which nickel superalloys can be used [Source 3] (which property and temperature was not checked here).

The rule-of-mixtures densities are about 13.6 g/cm³ for NbMoTaW and about 12.4 g/cm³ for VNbMoTaW (the table in Section 4); for comparison Ni is 8.91 and Ti is 4.51 g/cm³Our calculation. Where light weight is needed, high density can be a constraint on alloys that use refractory elements (Commentary).

Lightweight HEAs (Al-Li-Mg-Sc-Ti)

Youssef et al. made a low-density nanocrystalline alloy, Al₂₀Li₂₀Mg₁₀Sc₂₀Ti₃₀ (at.%), by mechanical alloying. It became single-phase fcc during ball milling and transformed to single-phase hcp on annealing; its estimated strength-to-weight ratio is reported to be significantly higher than other nanocrystalline alloys and comparable to ceramics, and high hardness is retained after annealingSourced [Source 11]. The rule-of-mixtures density is about 2.67 g/cm³Our calculation. But this is a nanocrystalline alloy made by mechanical alloying, and the strength is an “estimate”. The fracture toughness and ductility as a bulk structural material were not checked here.

TRIP-type dual-phase HEAs

The paper by Li et al. (Nature, 2016) showed a design that, the opposite of a “stable single phase”, deliberately lowers phase stability. In a metastable HEA (TRIP-DP-HEA) part of the fcc phase transforms to hcp martensite on plastic deformation; strength rises through the interfaces of the two phases and the transformation-induced hardening, and the greater capacity for strain hardening also raises ductility, so that it overcame the “trade-off” between strength and ductility. The paper states that HEAs were originally proposed expecting phase stabilisation through entropy maximisation, but, motivated by recent work that relaxes the strict restrictions on composition, it overturns that conceptSourced [Source 12]. The composition and the numerical strength and ductility were not checked here.

Materials engineer’s view 4: designs that drop “high entropy” are the way into practice

The alloy of Youssef et al. is not equiatomic (20, 20, 10, 20 and 30 at.%), and the alloy of Li et al. is deliberately metastable [Sources 11, 12]. Miracle and Senkov also say that “designing alloy families by selecting elements for a specific purpose has begun to emerge” [Source 3]. From a materials viewpoint, practical design is moving away from the definition “mix five or more elements equally” toward choosing elements from the target property (light weight, high-temperature strength, cryogenic toughness) (Commentary). When reading an HEA value, check not whether it fits the definition but whether it is a value compared with existing materials under the same conditions for the target property.

7. Additive manufacturing (laser powder bed fusion)

The review by Atabay et al. (High Entropy Alloys & Materials, 2024) summarises laser powder bed fusion (LPBF) of CoCrFeMnNi in terms of processing conditions, microstructure and mechanical properties. Reports listed include porosity below 0.01% at a volumetric energy density (VED) of 104 J/mm³, anisotropy by build direction in the as-built state, and about 50% higher elongation after hot isostatic pressing (HIP)Sourced [Source 13] (these are values from individual studies collected in the review, and the basis of comparison was not checked in detail here). Piglione et al. published a paper on the printability and microstructure of CoCrFeMnNi by LPBF (only the title was checked) [Source 14].

Terms in additive manufacturing are defined by ISO/ASTM 52900:2021 (Additive manufacturing — General principles — Fundamentals and vocabulary) [Source 26]. The definitions of individual terms were not checked here.

How to read this section

Additive-manufacturing values are fixed by the powder’s composition and size, the machine, the build conditions (power, speed, hatch spacing and layer thickness = VED), the build direction, and whether heat treatment or HIP followed. “CoCrFeMnNi can be built by LPBF” does not mean that pores, cracks and microstructural uniformity in the built part equal those of a cast part. Read tensile and toughness values together with the direction in which the specimen was built (the build direction against the loading direction) (Commentary).

8. Corrosion, hydrogen and radiation

Corrosion: The review by Shi et al. (Metals, 2017) organises the corrosion resistance of HEAs across various aqueous environments, HEA coatings, and the effects of environment, alloying elements and processing, and says that HEAs, with their locally disordered chemical environment, are expected to show unusual corrosion resistanceSourced [Source 15] (as the word “expected” shows, this is not a general advantage). The review by Atabay et al. collects a report that LPBF CoCrFeMnNi performed better than 316L in 3.5 wt% NaCl and not in 1 N H₂SO₄ [Source 13]. The ranking in corrosion resistance changes with the environment (the solution).

Hydrogen: Feng et al. compared CoCrFeMnNi with 304 stainless steel and IN718 under hydrogen charging and report that resistance to hydrogen embrittlement was highest for the HEA, followed by 304 and then IN718 (a difference in result between charging for 24 and for 48 hours is also shown, but the details were not checked here)Sourced [Source 17]. Zhao et al. published a paper on the resistance of CoCrFeMnNi to gaseous hydrogen embrittlement (only the title was checked) [Source 18]. The review by Atabay et al. carries a report that hydrogen permeation in LPBF CoCrFeMnNi was about five times smaller (the comparison was not checked here) [Source 13].

Radiation: Granberg et al., by experiment and modelling, showed that single-phase NiFe and NiCoCr accumulate much less damage under prolonged irradiation than elemental Ni, and explain it by lower dislocation mobility, which slows the growth of large dislocation structures. They also report no observable phase separation, ordering or amorphisationSourced [Source 16] (the type of irradiation and the dose were not checked here).

Materials engineer’s view 5: read corrosion, hydrogen and radiation comparisons together with “an existing material under the same conditions”

Corrosion comparisons move with the solution’s composition and concentration, temperature, specimen surface finish, polarisation sweep rate and hold time. ISO 17475:2005 is a guide to making potentiostatic and potentiodynamic polarisation measurements [Source 25]. Hydrogen embrittlement results change with the way and the time of charging and the test speed (as the statement that Feng et al. showed a difference between 24 and 48 hours indicates [Source 17]). Radiation damage means something only once the type of irradiation, temperature and dose are fixed. From a materials viewpoint, do not generalise that “HEAs excel in corrosion, hydrogen and radiation resistance”; read it as a comparison in a particular environment against a particular existing material (Commentary).

9. Limits, and what could not be confirmed

Depth of checking of primary sources: many papers were checked only to the level of their abstracts. The individual values of Cantor et al. (2004), Tsai et al. (2013), Senkov et al. (2011) and Li et al. (2016), and the papers of Piglione et al. (2018) and Zhao et al. (2017), were not checked in the body. The body of Gludovatz et al. (2016) and of Miracle et al. (2014) were checked
Lattice-distortion and cocktail effects: no statement testing these was found in primary sources, so no assessment is written
Boundary values of VEC: the fcc/bcc boundary values shown by Guo et al. could not be checked in the body, so they are not written
High-temperature strength and oxidation of refractory HEAs: temperature-by-temperature strength values and oxidation behaviour were not checked here
Other alloy systems: other high-entropy systems besides refractory HEAs (eutectic HEAs, complex concentrated alloys containing intermetallics), precipitation-strengthened HEAs and HEA coatings are outside this article
Practical products and markets: alloys in practical use, prices, supply, resources and recycling, and workability could not be confirmed in primary sources. Market-research estimates are not used
Standards specific to HEAs: no ISO, IEC, IEEE or JIS standard aimed at HEAs could be confirmed (Section 10)
This article is not advice on safety, regulation or medicine. The user of an alloy should check the specification and the laws that apply

10. How to read the evaluation standards

HEA evaluation uses tests of tension (room, high and cryogenic temperature), Charpy impact, fracture toughness (J-integral, KJIc), hardness, creep, grain size and polarisation measurement (corrosion). What standards define is the method of each test; they do not define “HEA” or give pass criteria for an alloy’s performance. No ISO, IEC, IEEE or JIS standard aimed at HEAs could be confirmed in this article.

Item	ISO	IEC / IEEE	JIS	ASTM	What changes the value with test conditions
Tension (room temperature)Sourced	ISO 6892-1:2019 (tensile testing of metallic materials, method at room temperature)	Could not be confirmed	JIS Z 2241 (method of tensile test for metallic materials)	E8 (described in papers as tensile testing; E8/E8M specimens also described; full title not confirmed)	Specimen shape and size, strain rate, grain size, processing state [6]
Tension (high temperature)Sourced	ISO 6892-2:2026 (method at elevated temperature, 3rd edition, 2026-08)	Could not be confirmed	Could not be confirmed	E21 (described in papers as high-temperature tension; title not confirmed)	Hold temperature and time, strain rate, atmosphere (watch oxidation of refractory HEAs)
CreepSourced	ISO 204:2023 (uniaxial creep testing in tension; uninterrupted and interrupted tests, stress rupture, and a test that a time can be exceeded)	Could not be confirmed	JIS Z 2271 (method of creep and creep rupture test for metallic materials)	Could not be confirmed	Stress, temperature, time, atmosphere
Charpy impactSourced	ISO 148-1:2016 (V-notch and U-notch; Annexes B and C based on ASTM E23; under revision)	Could not be confirmed	JIS Z 2242 (method for Charpy pendulum impact test of metallic materials)	E23 (described in papers as Charpy V-notch impact testing; full title not confirmed)	Notch shape, test temperature, specimen size [22]
Fracture toughness (K, δ, J, R-curves)Sourced	ISO 12135:2021 (unified method for quasistatic fracture toughness K, δ, J and R-curves)	Could not be confirmed	JIS Z 2284 (elastic-plastic fracture toughness JIC in liquid helium; a standard for the cryogenic range)	E1820 (described in papers as testing J-integral and CTOD resistance curves; Gludovatz et al. tested “in general accordance” [6])	Specimen (C(T)), pre-crack, side grooves, temperature, validity conditions, crack growth [6]
Hardness (Vickers)Sourced	ISO 6507-1:2023 (Vickers hardness test; indentation diagonals of 0.020 to 1.400 mm; includes coatings)	Could not be confirmed	JIS Z 2244-1 (Vickers hardness test — Part 1: Test method)	E384 (described in papers as micro-hardness testing; title not confirmed)	Test force, hold time, indentation size, specimen surface condition
Grain sizeSourced	Could not be confirmed	Could not be confirmed	Could not be confirmed	E112 (described in papers as line-intercept grain-size measurement; title not confirmed)	Method (intercept or area), whether twin boundaries count as grain boundaries (Commentary), number of fields measured
Polarisation measurement (corrosion)Sourced	ISO 17475:2005 (guidelines for potentiostatic and potentiodynamic polarisation measurements)	Could not be confirmed	Could not be confirmed	Could not be confirmed	Solution, temperature, sweep rate, surface finish (Commentary)
Terms for additive manufacturingSourced	ISO/ASTM 52900:2021 (additive-manufacturing vocabulary; ISO/TC 261)	Could not be confirmed	Could not be confirmed	A joint standard (ASTM is in the number; the ASTM site was not consulted)	A vocabulary standard, so no measurement conditions
Definition and notation of HEA compositionSourced	Could not be confirmed	Could not be confirmed	Could not be confirmed	Could not be confirmed	“Five or more elements, 5–35 at.% each” is the definition in a paper [4], not a standard’s definition

Standard numbers and titles were checked on official ISO pages for ISO and on the JIS search of the Japanese Industrial Standards Committee (JISC) for JIS; JIS titles are our translation of the Japanese titles. For ASTM standards, the ASTM website was not opened; only the number and the stated use were checked in the body of peer-reviewed papers. The ASTM column gives no test content, conditions or acceptance criteria. The arrangement of the table is Our calculation.

Where each standard sits — international, national, trade body

ISO is an international standard, JIS a national standard, and ASTM a trade standard issued by a US standards body. ISO 6892-1, JIS Z 2241 and ASTM E8 are all “tensile test” standards, but their degree of agreement (identical, modified and so on) could not be confirmed because their texts were not checked
ISO 6892-2 is current as the 2026 edition (3rd edition, August 2026), and the 2018 edition is withdrawn. ISO 6892-1 is the 2019 edition (3rd edition), confirmed as of 2025. ISO 148-1 is current as the 2016 edition and is under revision. The same number can carry a different procedure in a different edition
JIS Z 2284 is a standard for elastic-plastic fracture toughness in liquid helium (about 4 K); it is not the standard used in the paper of Gludovatz et al. in this article (77 K, liquid nitrogen). It is mentioned only to show that JIS has a standard for the cryogenic range

Cautions when reading

A standard is a “test method” and does not guarantee an alloy’s performance. “A tensile test to ISO 6892-1” is a value from that method; a different composition, processing or grain size gives a different value
A paper’s “following a standard” can mean following it in general. Gludovatz et al. wrote “in general accordance with ASTM E1820” [Source 6]. Whether the validity conditions were met is checked in the paper’s body
Read a cryogenic test with temperature, coolant and specimen size. The same paper shows strength, ductility and toughness changing across 293, 198 and 77 K [Source 6]
For corrosion, hydrogen and radiation, the description of conditions matters more than a standard value. No test standard specific to HEAs could be confirmed

11. Glossary

High-entropy alloy (HEA): In papers, an alloy of five or more elements at 5–35 at.% each [4]. In use the term is wider, and differs from multi-principal-element alloys (MPEAs) of three or more elements and complex concentrated alloys (CCAs).

Configurational entropy: Entropy from the disorder of atomic arrangement. For N equiatomic elements, R ln N.

Equiatomic: A composition in which every element has the same atomic fraction.

at.%: Atomic percent. Different from mass percent (wt%).

Solid solution: A state in which several elements are mixed within one crystal lattice.

Intermetallic compound: An ordered phase in which elements sit in fixed ratios. Often brittle.

fcc / bcc / hcp: Face-centred cubic, body-centred cubic and hexagonal close-packed crystal structures.

VEC (valence electron concentration): The mean number of valence electrons per atom. A guide to fcc/bcc stability [8].

Rule of mixtures (ROM): Estimating an alloy’s property as a weighted mean of its components’ properties.

Refractory HEA (RHEA): An HEA based on refractory elements such as Nb, Mo, Ta and W [10].

KJIc: Fracture toughness at crack initiation, converted from the J-integral (MPa√m).

Deformation twin (nanotwin): A twin formed by deformation. Linked to sustained strain hardening [5, 6].

TRIP: Transformation-induced plasticity: a phase transforms during deformation and ductility rises [12].

LPBF: Laser powder bed fusion: additive manufacturing that spreads powder and melts it with a laser.

HIP: Hot isostatic pressing: reducing internal pores at high temperature and pressure.

12. References (primary sources)

Yeh J.-W., Chen S.-K., Lin S.-J., Gan J.-Y. et al. “Nanostructured High-Entropy Alloys with Multiple Principal Elements: Novel Alloy Design Concepts and Outcomes”, Adv. Eng. Mater. 6, 299–303 (2004), DOI 10.1002/adem.200300567 (abstract checked) — doi.org/10.1002/adem.200300567
Cantor B., Chang I. T. H., Knight P., Vincent A. J. B. “Microstructural development in equiatomic multicomponent alloys”, Mater. Sci. Eng. A 375–377, 213–218 (2004), DOI 10.1016/j.msea.2003.10.257 (only the title, and what Gludovatz et al. say of it, were checked) — doi.org/10.1016/j.msea.2003.10.257
Miracle D. B., Senkov O. N. “A critical review of high entropy alloys and related concepts”, Acta Mater. 122, 448–511 (2017), DOI 10.1016/j.actamat.2016.08.081 (abstract checked) — doi.org/10.1016/j.actamat.2016.08.081
Miracle D. B., Miller J. D., Senkov O. N., Woodward C. et al. “Exploration and Development of High Entropy Alloys for Structural Applications”, Entropy 16, 494–525 (2014), DOI 10.3390/e16010494 (open access) — doi.org/10.3390/e16010494
Gludovatz B., Hohenwarter A., Catoor D., Chang E. H. et al. “A fracture-resistant high-entropy alloy for cryogenic applications”, Science 345, 1153–1158 (2014), DOI 10.1126/science.1254581 (abstract checked) — doi.org/10.1126/science.1254581
Gludovatz B., Hohenwarter A., Thurston K. V. S., Bei H. et al. “Exceptional damage-tolerance of a medium-entropy alloy CrCoNi at cryogenic temperatures”, Nat. Commun. 7, 10602 (2016), DOI 10.1038/ncomms10602 (open access) — doi.org/10.1038/ncomms10602
Tsai K.-Y., Tsai M.-H., Yeh J.-W. “Sluggish diffusion in Co–Cr–Fe–Mn–Ni high-entropy alloys”, Acta Mater. 61, 4887–4897 (2013), DOI 10.1016/j.actamat.2013.04.058 (only the title checked) — doi.org/10.1016/j.actamat.2013.04.058
Guo S., Ng C., Lu J., Liu C. T. “Effect of valence electron concentration on stability of fcc or bcc phase in high entropy alloys”, J. Appl. Phys. 109, 103505 (2011), DOI 10.1063/1.3587228 (abstract checked) — doi.org/10.1063/1.3587228
Senkov O. N., Wilks G. B., Scott J. M., Miracle D. B. “Mechanical properties of Nb25Mo25Ta25W25 and V20Nb20Mo20Ta20W20 refractory high entropy alloys”, Intermetallics 19, 698–706 (2011), DOI 10.1016/j.intermet.2011.01.004 (only the title checked) — doi.org/10.1016/j.intermet.2011.01.004
Couzinié J.-P., Senkov O. N., Miracle D. B., Dirras G. “Comprehensive data compilation on the mechanical properties of refractory high-entropy alloys”, Data in Brief 21, 1622–1641 (2018), DOI 10.1016/j.dib.2018.10.071 (open access) — doi.org/10.1016/j.dib.2018.10.071
Youssef K. M., Zaddach A. J., Niu C., Irving D. L. et al. “A Novel Low-Density, High-Hardness, High-entropy Alloy with Close-packed Single-phase Nanocrystalline Structures”, Mater. Res. Lett. 3, 95–99 (published online 2014), DOI 10.1080/21663831.2014.985855 (abstract checked) — doi.org/10.1080/21663831.2014.985855
Li Z., Pradeep K. G., Deng Y., Raabe D. et al. “Metastable high-entropy dual-phase alloys overcome the strength–ductility trade-off”, Nature 534, 227–230 (2016), DOI 10.1038/nature17981 (opening of the body checked) — doi.org/10.1038/nature17981
Atabay S. E., Sarafan S., Islam A., Bernier F. et al. “Laser Powder Bed Fusion Printing of CoCrFeMnNi High Entropy Alloy: Processing, Microstructure, and Mechanical Properties”, High Entropy Alloys & Materials 2, 129–173 (2024), DOI 10.1007/s44210-024-00035-1 — doi.org/10.1007/s44210-024-00035-1
Piglione A., Dovgyy B., Liu C., Gourlay C. M. et al. “Printability and microstructure of the CoCrFeMnNi high-entropy alloy fabricated by laser powder bed fusion”, Mater. Lett. 224, 22–25 (2018), DOI 10.1016/j.matlet.2018.04.052 (only the title checked) — doi.org/10.1016/j.matlet.2018.04.052
Shi Y., Yang B., Liaw P. K. “Corrosion-Resistant High-Entropy Alloys: A Review”, Metals 7, 43 (2017), DOI 10.3390/met7020043 (open access, abstract checked) — doi.org/10.3390/met7020043
Granberg F., Nordlund K., Ullah M. W., Jin K. et al. “Mechanism of Radiation Damage Reduction in Equiatomic Multicomponent Single Phase Alloys”, Phys. Rev. Lett. 116, 135504 (2016), DOI 10.1103/PhysRevLett.116.135504 (abstract checked) — doi.org/10.1103/physrevlett.116.135504
Feng Z., Li X., Song X., Gu T. et al. “Hydrogen Embrittlement of CoCrFeMnNi High-Entropy Alloy Compared with 304 and IN718 Alloys”, Metals 12, 998 (2022), DOI 10.3390/met12060998 (open access) — doi.org/10.3390/met12060998
Zhao Y., Lee D.-H., Seok M.-Y., Lee J.-A. et al. “Resistance of CoCrFeMnNi high-entropy alloy to gaseous hydrogen embrittlement”, Scr. Mater. 135, 54–58 (2017), DOI 10.1016/j.scriptamat.2017.03.029 (only the title checked) — doi.org/10.1016/j.scriptamat.2017.03.029
International Organization for Standardization (ISO) ISO 6892-1:2019 “Metallic materials — Tensile testing — Part 1: Method of test at room temperature” (3rd edition, 2019-11, confirmed as of 2025) — iso.org/standard/78322
International Organization for Standardization (ISO) ISO 6892-2:2026 “Metallic materials — Tensile testing — Part 2: Method of test at elevated temperature” (3rd edition, published 2026-08; the previous ISO 6892-2:2018 is withdrawn) — iso.org/standard/87885
International Organization for Standardization (ISO) ISO 204:2023 “Metallic materials — Uniaxial creep testing in tension — Method of test” — iso.org/standard/82162
International Organization for Standardization (ISO) ISO 148-1:2016 “Metallic materials — Charpy pendulum impact test — Part 1: Test method” (Annexes B and C are stated to be based on ASTM E23 and used with ASTM’s permission; under revision) — iso.org/standard/63802
International Organization for Standardization (ISO) ISO 12135:2021 “Metallic materials — Unified method of test for the determination of quasistatic fracture toughness” — iso.org/standard/78208
International Organization for Standardization (ISO) ISO 6507-1:2023 “Metallic materials — Vickers hardness test — Part 1: Test method” (5th edition, 2023-10) — iso.org/standard/83898
International Organization for Standardization (ISO) ISO 17475:2005 “Corrosion of metals and alloys — Electrochemical test methods — Guidelines for conducting potentiostatic and potentiodynamic polarization measurements” (2005-10, confirmed) — iso.org/standard/31392
International Organization for Standardization (ISO) ISO/ASTM 52900:2021 “Additive manufacturing — General principles — Fundamentals and vocabulary” (2nd edition, 2021-11, confirmed in 2025; ISO/TC 261) — iso.org/standard/74514
Japanese Industrial Standards Committee (JISC) JIS search “JIS Z 2241 Method of tensile test for metallic materials” (title translated from the Japanese) — jisc.go.jp (Z2241)
Japanese Industrial Standards Committee (JISC) JIS search “JIS Z 2242 Method for Charpy pendulum impact test of metallic materials” (title translated from the Japanese) — jisc.go.jp (Z2242)
Japanese Industrial Standards Committee (JISC) JIS search “JIS Z 2244-1 Vickers hardness test — Part 1: Test method” (title translated from the Japanese) — jisc.go.jp (Z2244-1)
Japanese Industrial Standards Committee (JISC) JIS search “JIS Z 2271 Method of creep and creep rupture test for metallic materials” (title translated from the Japanese) — jisc.go.jp (Z2271)
Japanese Industrial Standards Committee (JISC) JIS search “JIS Z 2284 Method of elastic-plastic fracture toughness JIC testing of metallic materials in liquid helium” (title translated from the Japanese) — jisc.go.jp (Z2284)
Public material used to confirm ASTM numbers and the uses stated for them (the ASTM website was not consulted): E8 in Materials 18, 1288 (2025), DOI 10.3390/ma18061288 (room-temperature tension to ASTM E8 and 760 °C tension to ASTM E21 are stated) / E23 in Nanomaterials 16, 66 (2026), DOI 10.3390/nano16010066 (Charpy V-notch impact tests to ASTM E23-18 are stated) / E1820 in Materials 18, 1051 (2025), DOI 10.3390/ma18051051 (E1820 is stated to have been developed for testing plane-strain initiation toughness or resistance curves in terms of the J-integral or CTOD) / E112 in PLOS One 21, e0354359 (2026), DOI 10.1371/journal.pone.0354359 (grain size measured by the ASTM E112 line-intercept method is stated) / E384 in iScience 29, 116678 (2026), DOI 10.1016/j.isci.2026.116678 (micro-hardness testing to ASTM E384-17 is stated) — doi.org/10.3390/ma18061288 (and others)

13. Claim-to-source audit

Claim in the text	Basis	Class
The standard definition of an HEA (five or more elements, 5–35 at.% each), ΔSconf = R ln N, 1.61R for N = 5 and 2.57R for N = 13, the values for conventional alloys (about 0.22R for low-alloy steels, about 1.15R for stainless steels, up to about 1.37R for superalloys), and the guide of 1.5R or more	Body of Miracle et al. (2014), checked in the browser Reference 4 https://doi.org/10.3390/e16010494	Sourced
The mean ΔG of binary compounds of about −41 kJ/mol (median −36), the share of binary intermetallics losing stability (about 10–15% at 300 K, about 20–32% at 600 K, about 40–60% at 1,500 K), the share of single-phase HEAs (about 1/3 at 600 K, about 2/3 at 1,500 K), CoCrFeMnNi single-phase and TiCrFeMnNi intermetallic	Body of Miracle et al. (2014), checked in the browser Reference 4 https://doi.org/10.3390/e16010494	Sourced
The “high-entropy effect” and “sluggish diffusion” not supported by the data; the microstructural assessment from 408 alloys and two CALPHAD datasets; seven CCA families; austenitic stainless steels and nickel alloys within MPEAs; some refractory alloys that may extend the range of nickel superalloys	Abstract of Miracle and Senkov (2017) Reference 3 https://doi.org/10.1016/j.actamat.2016.08.081	Sourced
The proposal of multi-principal-element alloys under the name “high-entropy alloys”, and the preliminary results of simple crystal structures, nanostructures and promising mechanical properties	Abstract of Yeh et al. (2004) Reference 1 https://doi.org/10.1002/adem.200300567	Sourced
The title of Cantor et al. (2004); that a 20-element equiatomic alloy was a brittle multiphase material and that CrMnFeCoNi was introduced in 2004 (as stated in the citation by Gludovatz et al.)	Title of Cantor et al. (2004); the statements are from the body of Reference 6 Reference 2 https://doi.org/10.1016/j.msea.2003.10.257	Sourced
CrMnFeCoNi as a single-phase fcc solid solution with tensile strength above 1 GPa and toughness above 200 MPa√m, properties improving at cryogenic temperature, the shift from planar slip to nanotwinning, continuous strain hardening	Abstract of Gludovatz et al. (2014) Reference 5 https://doi.org/10.1126/science.1254581	Sourced
CrCoNi (about 1 GPa, about 70% and KJIc above 200 at 293 K; above 1.3 GPa, up to 90% and 275 at 77 K), body KJIc (208 and 273 MPa√m), arc melting, 1,200 °C for 24 hours, about 60% reduction, 800 °C for 1 hour, grain size 5–50 μm, 293, 198 and 77 K, C(T) specimens and general accordance with ASTM E1820, CrMnFeCoNi 763 to 1,280 MPa, 0.5 to 0.7, KJIc above 200	Body of Gludovatz et al. (2016), checked in the open-access full text at Europe PMC Reference 6 https://doi.org/10.1038/ncomms10602	Sourced
The title of a paper on sluggish diffusion in Co-Cr-Fe-Mn-Ni	Title of Tsai et al. (2013) only Reference 7 https://doi.org/10.1016/j.actamat.2013.04.058	Sourced
The mixing enthalpy as the key factor deciding solid solutions or compounds, and fcc/bcc stability well delineated by VEC	Abstract of Guo et al. (2011) Reference 8 https://doi.org/10.1063/1.3587228	Sourced
The title of a paper on the mechanical properties of Nb25Mo25Ta25W25 and V20Nb20Mo20Ta20W20	Title of Senkov et al. (2011) only Reference 9 https://doi.org/10.1016/j.intermet.2011.01.004	Sourced
The data compilation of 122 RHEAs and RCCAs (2010 to January 2018), the definitions of RHEA and RCCA, and density and Young’s modulus computed by the rule of mixtures	Body of Couzinié et al. (2018), open-access full text at Europe PMC Reference 10 https://doi.org/10.1016/j.dib.2018.10.071	Sourced
Mechanical alloying of Al20Li20Mg10Sc20Ti30, the fcc-to-hcp transformation, the estimated strength-to-weight ratio, and hardness after annealing	Abstract of Youssef et al. (2014) Reference 11 https://doi.org/10.1080/21663831.2014.985855	Sourced
A metastable TRIP-type dual-phase HEA, the martensitic fcc-to-hcp transformation, the simultaneous gain in strength and ductility, and the move away from “stabilisation by entropy maximisation” in design	Opening of the body of Li et al. (2016) Reference 12 https://doi.org/10.1038/nature17981	Sourced
LPBF of CoCrFeMnNi (VED 104 J/mm³, porosity below 0.01%, anisotropy by build direction, about 50% higher elongation after HIP), the corrosion comparison with 316L (3.5 wt% NaCl and 1 N H2SO4), and a report of about five times smaller hydrogen permeation	Review by Atabay et al. (2024) (details of the basis of comparison not checked) Reference 13 https://doi.org/10.1007/s44210-024-00035-1	Sourced
The title of a paper on the printability and microstructure of CoCrFeMnNi by LPBF	Title of Piglione et al. (2018) only Reference 14 https://doi.org/10.1016/j.matlet.2018.04.052	Sourced
A review of the corrosion resistance of HEAs (aqueous environments, coatings, and unusual corrosion resistance expected from a locally disordered chemical environment)	Abstract of Shi et al. (2017) Reference 15 https://doi.org/10.3390/met7020043	Sourced
Much less accumulated irradiation damage in single-phase NiFe and NiCoCr than in Ni, lower dislocation mobility, and no phase separation, ordering or amorphisation observed	Abstract of Granberg et al. (2016) Reference 16 https://doi.org/10.1103/physrevlett.116.135504	Sourced
Resistance of CoCrFeMnNi to hydrogen embrittlement higher than 304 and IN718, and the difference in result with hydrogen-charging time	Feng et al. (2022) (details not checked) Reference 17 https://doi.org/10.3390/met12060998	Sourced
The title of a paper on the resistance of CoCrFeMnNi to gaseous hydrogen embrittlement	Title of Zhao et al. (2017) only Reference 18 https://doi.org/10.1016/j.scriptamat.2017.03.029	Sourced
The number, title and scope of ISO 6892-1:2019	Official ISO page Reference 19 https://www.iso.org/standard/78322.html	Sourced
The number, title and edition of ISO 6892-2:2026 (3rd edition, 2026-08)	Official ISO page Reference 20 https://www.iso.org/standard/87885.html	Sourced
The number, title and scope of ISO 204:2023	Official ISO page Reference 21 https://www.iso.org/standard/82162.html	Sourced
The number, title and scope of ISO 148-1:2016 (Annexes B and C based on ASTM E23)	Official ISO page Reference 22 https://www.iso.org/standard/63802.html	Sourced
The number, title and scope of ISO 12135:2021	Official ISO page Reference 23 https://www.iso.org/standard/78208.html	Sourced
The number, title and scope of ISO 6507-1:2023 (range of indentation diagonals)	Official ISO page Reference 24 https://www.iso.org/standard/83898.html	Sourced
The number, title and scope of ISO 17475:2005	Official ISO page Reference 25 https://www.iso.org/standard/31392.html	Sourced
The number, title and status of ISO/ASTM 52900:2021 (confirmed in 2025)	Official ISO page Reference 26 https://www.iso.org/standard/74514.html	Sourced
The number and title of JIS Z 2241 (method of tensile test for metallic materials)	JIS search of JISC Reference 27 https://www.jisc.go.jp/app/jis/general/GnrJISNumberNameSearchList?show&jisStdNo=Z2241	Sourced
The number and title of JIS Z 2242 (method for Charpy pendulum impact test of metallic materials)	JIS search of JISC Reference 28 https://www.jisc.go.jp/app/jis/general/GnrJISNumberNameSearchList?show&jisStdNo=Z2242	Sourced
The number and title of JIS Z 2244-1 (Vickers hardness test — Part 1: Test method)	JIS search of JISC Reference 29 https://www.jisc.go.jp/app/jis/general/GnrJISNumberNameSearchList?show&jisStdNo=Z2244-1	Sourced
The number and title of JIS Z 2271 (method of creep and creep rupture test for metallic materials)	JIS search of JISC Reference 30 https://www.jisc.go.jp/app/jis/general/GnrJISNumberNameSearchList?show&jisStdNo=Z2271	Sourced
The number and title of JIS Z 2284 (method of elastic-plastic fracture toughness JIC testing of metallic materials in liquid helium)	JIS search of JISC Reference 31 https://www.jisc.go.jp/app/jis/general/GnrJISNumberNameSearchList?show&jisStdNo=Z2284	Sourced
The numbers of ASTM E8, E21, E23, E1820, E112 and E384 and the uses stated for them in papers (the ASTM site was not consulted; checked in the body of peer-reviewed papers; the full titles of E21, E384 and E8 could not be confirmed)	Statements in peer-reviewed open-access papers Reference 32 https://doi.org/10.3390/ma18061288 (and others listed at the end of the references)	Sourced
The values of ΔSconf/R (N = 2 to 13 and 20; about 1.56 for the non-equiatomic Al20Li20Mg10Sc20Ti30), the entropy term −TΔSconf (300, 600, 1,000 and 1,500 K, N = 2, 5 and 13), and its ratio to the mean ΔG (about one third)	Our calculation. Ideal configurational entropy only, with R = 8.314 J/(mol·K); mixing enthalpy and strain energy are not included	Our calculation
VEC (CoCrFeMnNi 8.0, NbMoTaW 5.5, VNbMoTaW 5.4, Al20Li20Mg10Sc20Ti30 2.8) and rule-of-mixtures densities (about 8.0, 13.6, 12.4 and 2.67 g/cm³)	Our calculation. The valence electron counts, standard atomic masses and elemental densities are standard values used in this article. They are not measured densities	Our calculation
The change from 293 K to 77 K (about 1.68 times for the tensile strength of CrMnFeCoNi, about 1.31 times for KJIc of CrCoNi, a 20-point rise in failure strain)	Our calculation. Ratios of values from different papers and specimens, not ratios within one test	Our calculation
The arrangement as “four core effects”, the way the assessments are laid out, and the readings “a single phase needs a check of the state”, “read cryogenic values by deformation mechanism, grain size and test conditions”, “designs that drop high entropy are the way into practice” and “compare corrosion, hydrogen and radiation with an existing material under the same conditions”, and the organisation of Fig. 4	This article’s own organisation and interpretation of published content; not the views of the authors of each paper (“probably linked to a low stacking-fault energy” is an inference beyond the papers’ statements)	Commentary
The assessment of the lattice-distortion and cocktail effects, the boundary values of VEC, the high-temperature strength and oxidation of refractory HEAs, standards specific to HEAs, corresponding IEC and IEEE standards, practical products, prices and markets, values for comparison materials, and the full titles of ASTM E21, E384 and E8	Could not be confirmed in the primary sources accessible within this article’s survey, so not stated	Commentary
That Figs. 2, 3, 4 and 6 are explanatory drawings, not real observations or data, and that Figs. 1 and 5 are AI-generated images	This article’s note	Commentary

Last updated 10 October 2026. Sources are limited to primary material (peer-reviewed papers and standards-body pages). Many papers were checked only to the extent of their abstracts; the bodies of Gludovatz et al. (2016), Miracle et al. (2014) and Couzinié et al. (2018) were checked. Because the article includes structural readings and materials-design interpretations, those are marked as Commentary and kept separate from sourced fact. The assessment of the lattice-distortion and cocktail effects, the boundary values of VEC, the high-temperature strength and oxidation of refractory HEAs, standards specific to HEAs, and practical products, prices and markets could not be confirmed and are not stated here. HEA figures are laboratory results with composition, processing, grain size and test temperature fixed, and cannot be generalised to other alloys or real use. All figures are explanatory concept graphics. Figs. 2, 3, 4 and 6 are vector drawings; Figs. 1 and 5 are AI-generated images, and none of them shows a real micrograph, experimental data or physical product.